PSR1

PSR-1, or PHP Standards Recommendation 1, Basic Coding Standard, is a PHP-FIG standard that defines a minimal set of rules intended to improve interoperability of PHP code across projects. It focuses on basic file structure, encoding, and namespace usage rather than on stylistic details. The standard is designed to be lightweight and to complement more prescriptive standards such as PSR-2 (Coding Style Guide) and PSR-4 (Autoloading).

Key points include that files should use UTF-8 encoding without BOM; PHP code should be contained in PHP tags, with the use of short open tags discouraged; and if a file declares any classes, interfaces, functions, or constants, it should declare a namespace, with code in the global namespace avoided where possible. PSR-1 also encourages code to be organized in a way that supports autoloading, making it easier for autoloaders to locate classes by their fully qualified names.

Impact and usage: PSR-1 has been widely adopted as a baseline in PHP frameworks and libraries, often referenced in coding guidelines and continuous integration checks to ensure cross-project compatibility.

History: The PHP Framework Interop Group (PHP-FIG) published PSR-1 as part of a family of standards to promote interoperability among PHP projects. It is intended to be stable and to evolve as the ecosystem grows.